1. Field of the Invention
The invention relates to a monopole slot antenna structure, and particularly relates to a monopole slot antenna structure having a tuning slot section for conveniently adjusting suitable frequencies, and the monopole slot antenna structure being capable of operating in dual-frequency environment.
2. Description of Related Art
As Internet develops vigorously, various kinds of network platform services, such as networked communication platforms (for example, message boards, forums, community websites and so forth) or data exchange platforms (for example, web albums, official download spaces, networked space and so forth) or personal service platforms (for example, electronic mailboxes, blogs, web games and so forth), all have been involved with everyone's lives. As such, these network platform services make it convenient for people to obtain necessary data when they are at home or in working environments. In particular, prevalence of wireless communications revolves the problem in which people can only use Internet in a particular area due to length limitations of physical connections. Therefore, communication devices with wireless communication functionality such as mobile phones, personal digital assistants (PDA) or tablet computers have gradually become necessity in people's lives.
Accordingly, in current communication devices, Wi-Fi™, one of most commonly used wireless communication protocol standards, is based on IEEE 802.11 standards. Wi-Fi™ operates in 2.4 GHz frequency band (802.11 b/g/n) and 5 GHz frequency band (802.11 a/n). Since people mainly require exterior designs of communication devices to be light, slim, short and small, vendors mainly concern simplification of electronic components or shortening of built-in antenna length in design of communication devices supporting Wi-Fi™, in order to meet the aforementioned design requirements. In general, most of the vendors currently apply a monopole antenna as the built-in antenna of the communication devices since the monopole antenna has simple structure and its resonance frequency is a quarter of wavelength of the operating frequency. As such, the length of the monopole antenna is shorter. An electric current generated in a closed loop due to potential difference on the antenna makes the antenna function normally. Thus, the ground point of the electric circuit board or the body of the electronic device are usually taken as a reference ground plane of the monopole antenna. Nonetheless, any electronic components or conductors closer to the monopole antenna may influence the monopole antenna, such as forming a closed electric circuit accidentally. As such, signal quality of the electromagnetic signals received by the monopole antenna may be poor. Thus, in order to maintain good antenna functionality, the vendors seem to allocate a larger clearance area around the monopole antenna, but such allocation design will greatly increase an overall volume of the communication device.
In order to resolve the monopole antenna being too sensitive or easily influenced by surrounding objects, some vendors attempt to use a slot antenna to be the antenna of the communication device operating in dual-frequencies, since the slot antenna is not easily influenced by neighbouring electronic components or conductors. As such, it is not necessary for the vendors to allocate an additionally larger clearance area around the slot antenna. However, the resonance frequency of the slot antenna is a half of the wavelength of the operating frequency. Thus, the required antenna length is far greater than that of the monopole antenna, for example, under the same operating frequency, the length of the slot antenna is twice of that of the monopole antenna, so the overall volume of the communication device cannot be greatly reduced. Further, the slot antenna is usually a long rectangular metal frame, where there will be a long rectangular slot allocated being extended in the same direction as the long rectangular metal frame in the middle of the long rectangular metal frame. The vendors may tune a plate width between the long rectangular metal frame and the long rectangular slot, in order to adjust effects of high operating frequencies and low operating frequencies. However, in the aforementioned tuning, the location where the long rectangular metal frame corresponding to a short edge of the long rectangular slot has two tuning widths, while the location where the long rectangular metal frame corresponding to the a long edge of the long rectangular slot has fourth tuning widths. All these tuning widths will interactively influence characteristics of high operating frequencies and low operating frequencies. Therefore, the vendors require spending longer operation time for tuning the slot antenna to an expected operating frequency, which greatly lowers operation efficiency of the vendors.
Based upon the aforementioned, no matter a monopole antenna or a slot antenna, which are all limited by antenna characteristics thereof, cannot be properly designed for allocation communication devices of small volumes. Therefore, in order to revolve the aforementioned drawbacks of the conventional art, it is a major issue for related antenna design vendors to design an antenna with a shorter length and with operating frequency which can be easily tuned.